Granular fertilizers and processes for making them



. Nov. 4, 1958 J. MoYRAND ETAL GRANULAR FERTILIZERS AND PROCESSES FOR MAKINGv lI-IEIM Filed July 9. 1952 mmJOOu United States Patent Oce GRANULAR FERTILIZERS AND PROCESSES FOR MAKING THEM Jean Moyrand, Chauny, `and Bernard Bigot, Rouen,

France, assignors to Societe Anonyme des Manufactures des Glaces et Produits Chimiques de Saint- Gobain, Chauny & Cirey, Paris, France Application July 9, 1952, Serial No. 297,872

Claims priority, application France July 24, 1951 12 Claims. (Cl. 71-64) This invention relates to fertilizers, primarily, but the principles thereof are applicable to the granulaton of various salts from solutions or, particularly, from sludges which are rich in Water, that is to say, which are capable because of their content of liquid of dissolving some of the final product of the process. As the invention solves a number of problems in the difficult process of preparing granular fertilizers it will be described in connection with that manufacture.

The first step in the standard process of producing fertilizer is to attack natural phosphate of fertilizer grade with an acid. Examples of such phosphates are the natural phosphates of Morocco and Florida. Phosphates of fertilizer grade also include some by-products of certain industries, such as phosphatic slags from the iron and steel industries, but most of it is of natural Origin. The acids usually employed toopen the phosphate are sulfuric acid and nitric acid, which are used alone or in combination. The employment of nitric acid either alone or in combination makes a process which is of particular diculty, beset by losses of valuable ingredients, and plagued with great ditliculties of granulation. As this is the most difficult of the fertilizer processes, the invention will be described in relation to it, but without restricting the generality of its application.

During the process of manufacturing fertilizer bythe methods of the prior art, the natural phosphate, which is most generally used, is attacked by acid, producing a sludge which is subjected directly to granulation, but before that can be accomplished, it is necessary to incorporate with the sludge a large amount of dry material, and that dry material is generally obtained from the nal product of the process itself, thatl is, completed fertilizer is added to the sludge. Thus, a large part of the nished product has to pass at least twice through the apparatus and steps of the process and, for the purposes of this specication, the finished product thus returned is called the re-cycled product.

For reasons which are well-known in the industry, it is desirable to sell a granulated product of Which the granules are of like size, consequently the product is screened at the end of the process and the oversized particles, those which are larger than the size which it is desired to market, and the undersizcd particles, those which are smaller, are re-cycled. The large particles are crushed or otherwise broken and reduced in size before they are admitted to the process again, These operations require handling and a contribution of additional energy, which is the greater as the re-cycled product attains live to six times the weight of the product which is produced by the factory in marketable condition. The processes f the prior art may, consequently, be accused, with some justice, of gross ineiciency which acts strongly to elevate the price of the product.

Another difficulty is that during the reduction in size of the oversized particles, which are generally insuiiciently dried, the apparatus is frequently halted by the clogging of screens and breakers. processes were generally unstable or unbalanced; for instance, occasionally the relative quantity of lines or of oversized particles increased so that the quantity `of re-cycled product increased While the quantity of new material supplied by the acidication of the rock did not increase, and the reintroduction of these exceptionally large quantities upset the granulation so that there was a greater and greater unbalance. This unbalance would increase until it stopped all granulation unless the condition Was immediately recognized and corrected by the addition of Waterto the sludge. It was extremely difficult to make such additions of Water with any accuracy.

In order to overcome these difficulties, the prior art has proposed to reduce the quantity of re-cycled product by concentrating the sludges to a maximum before introducing them into the granulator, but it has been the experience of all fertilizer manufacturers that those concentration operations are difficult to carry out, and that it is not possible to attain the necessary concentrations with some fertilizers. g

It is an object of this invention to eliminate the preliminary concentration which was an essential characteristie of the improved processes of the prior art. Another object of the invention is to reduce the quantity of product which is re-cycled. Another object is to improve the regularity and controllability of the process and to improve the thermal eiiciency of the process and the productive capacity of the apparatus.

The invention involves a new process, and a` new apparatus conceived for the carrying out of the process.

yAccording to our invention, our novel process begins with the sludge Which is produced by the acidificationl of phosphate of fertilizer grade. This sludge should be iluid, containing enough Water to be capable of dissolving some of the fertilizer produced by the process. In the example hereinafter given, the sludge contained 28% Water. The 28% of Water found in the accompanying example is not a limitation; the basic requirement for the sludge is that it shall contain enough Water to dissolve some of the iinal product. The sludges that are produced by the normal acidiication processes of the prior art, generally contain such a quantity of Water.

Of course, to obtain the optimum result, it is advisable to produce a sludge having a uniform quantity of Water, as this makes for a process of superior efficiency. What constitutes an optimum quantity of Water will vary according to the type of fertilizer which is being made, to the acids which are employed, their nature and their strength, and to what materials may be added to the sludge, for instance, phosphoric acid, prior to its employmentk in granulation. Consequently, for general purposes of this invention it may be stated that the invention proceeds Well if one begins by employing a sludge produced by a process of the prior art, i. e. containing from l5 to 35 of Water.

Another step of the new process requires the division of the product issuing from the process into three sizes, an average size, otherwise called commercial size, which in the example consists of granules from 2 to 4 millimeters in diameter, fines or undersized particles-which are smaller than 2 millimeters in diameter and gross or oversized granules which are larger than 4 millimeters in diameter. In the preferred form of the invention, the

cling, being mixed with the sludge at a stage Where it contains enough water to reduce the size of the coarse particles by dissolving their outer parts, or even to dissolve` them completely. When only the outer parts are dis-" Patented Nov. 4, 1958` Furthermore, the prior art` solved there is an immediate advantage that the particle sizeA of the oversized re-cycled granules may be reduced' to the average dimensions which are desired for sale.

lSome of the, granules maybe totally dissolved, but this does no harml asthe particles again appear as granules in a later stagel off the process. Thus, in this stage of the process,- the oversized particles are reduced to the desired be maintained at a'maxirnum, the mixing of the re-cycledproduct-with the sludge should be at a place where the slndgeisat the highest temperature possible, i. e. slightly belowY the boiling point and practically between 8() and 100 C; Advantageously the recycling should take place where--exothennic reactions are proceeding and the recycled product should be returned while it is as hot as possible, for instance, as soon as it issues from the granulator or the dryer. A particularly valuable phase of the invention arises when the fertilizer is to be ammoniated, as the ammoniation is accompanied by the liberation of heat; soV that if the ammoniation and the re-cycling occur at the same place, in the same. vat, a Valuable andeconomic'heat exchange occurs which improves the eficiency ofthe process. If, in a particular case, additional heat is needed itcan be added by any suitable means to keep the process at peak eiciency. v

VThe addition of the oversized particles -to the process by re-cycling can be accomplished advantageously in two stages as will be more particularly pointed out in the followingexample. This is advantageous but notnecessary.

In what we will call the fourth step of the process for purposes of nomenclature, the undersized particles, called nes, from the screening of the finished product, are returned, to a later stage, or to later stages, of the process, than those which have been referred to as receiving the re-cycled oversized granules. In this case, it is preferred that the fines be introduced in Stages, the nest fines being introduced'last. This step can also be accompanied by the introduction of other solids which may enter into the composition of the fertilizer, for instance, the introduction of potassium salts, or the product of averagesize may be crushed and added if an advantage isgained thereby. Whereas the introduction of the oversized particles as above described maydesirably be accompanied by heating, the addition of the nes to the later stages of the process may desirably be accompanied by cooling. The re-cycling of the tinestnes and of thefcrushed granules of medium size, if such are employed, desirably takes place at a temperature from about 5() to 75 C.

The product issuing from the granulation stage proceeds to a dryer and the dried product is sent to a screen fromn whence the large particles are re-cycled as above described, those which pass through the screen are preferably cooled, and thence sent to another screenwhich separates the nes from the particles of the size desired `for commerce.

The new. process overcomes the imperfections of the priorart which have been mentioned hereinabove and in particular reduces the quantity of re-cycled product without having to undertake a preliminary concentration of the sludge. It also reduces the irregularities in quality and quantity which were characteristic of the prior art. Furthermore, the thermal Veieiency of the process and the productive .capacity of the apparatus are much improved.

In principle, the invention involves dividing the recycled product in several fractions which are-added to the sludge in diierent states or stages of the manufacture, these states or stages being selected according tothe gran*- ulancondition of theI fractions, thatA is to say, the size thereof.v In practice, the product which issues from the granulator or from the dryer is separated into oversized granules, granules of' the size which are desiredV for the market, and under-sized granules. The oversized gran-` ules are re-cycled to a stage of the process where the sludge is still sufficiently uid to dissolve it, at least-n part, thus reducing the dimensions to those which are desiredv for sale; the iines are re-cycled to-the sludge at'a later stage of manufacture where'the sludge is suciently Y concentrated to `crystallize on the fines and to increase their dimensions to the size desired in the final product.

As the dissolving of the oversized granules in the sludge includes a lowering of the temperature which tends to oppose the eflciency ofthe solution, measures are taken to compensate for this lowering of'the temperature; thus,

one may re-cycle the over-sized granules to a stage of the process in which the sludge is undergoing exothermic chemical reaction. In addition, the over-sized granules may be re-.cycled while as hot as possible, that is, just asV they issue from the granulator or. the dryer.. Fina1ly,`jif these means are insufficient exterior heating can be resortedV to,.for instance, blowing thel reaction mass with hot air.

On the other hand, the reintroductionV off the iinesis* made under such condition that they produce a crystallization of the sludge, which is exothermic, and consequently, this stage of the process is preferably accompanied'by any' suitable means of refrigeration; a particularly satisfac-` toryv method is to refrigerate the nes before they are recycled, .as this requires refrigeration only of the material:4 of the nes and not of theentire mass inthe sludge;-v

the addition ofiines to the sludge may receive'othensolid materials which will enter beneficially into `the composi-` tion of .the fertilizer, such-as, forV example, supplemental fertilizers a fraction of the saleable-product-after prelimv inary crushing or othersize reduction.

This latter step can bel employed, asillustrateddn thefollowing example, to assure theregularity of the process.

The .apparatus of novel conception which is employed-U intheoperation of this process is shown in-theaccompanying drawing, and is characterisedl in that the usualV mixer-granulator heretofore employedfor the granulationsf is replaced by three distinct apparatus: The iirst ofl these three distinct apparatus is called, fori convenience,`v

a dissolver-concentrator, in whichthe recycled oversized granules are dissolved by the sludge atthe same time;` This. ap.-l t paratus advantageously is of large size and-is provided'` that they assistiin concentrating'the sludge.

with agitators and preferably with a-hot-air heatingfsystem for maintaining the temperature at about`v `tol C. It is supplied with sludge rich in: water. as" above 'dei-ined' 1and with oversized particles from' thenaL screening. It is satisfactory to discharge the product fromthis vat by over-flow. When the preparationof-'the' sludge includes a chemical'reaction which. releases heat,

for the tendency of the Vprocess `of solution temperature of the sludge.v

A mixer is connectedtothe `discharge overtlowportof`z the 'dissolver-concentrator: so V:that the product y discharged at the end vof one isreceived-at thezheadof"tirev Gthe The Sludge,k Concentrated p and.' thickened 1 by partial@V`` the mixer. `If this does not suice, a blast of cold air l can be directed upon the mixture in the mixer. From the end ofv the mixture the product is directed to a granulator ywhere the temperature should be preferably maintained in the range from about 40 to 65 C. The granulators of the prior art, particularly those having vigorous action, are satisfactory at this stage ofthe process.

In the case discussed hereinabove, where the fines are' introduced in two distinct fractions, the premier is preferably introduced into the mixer, and the thickened paste issuing from the mixer into the granulator receives the ;second fraction, the smallest nes in the re-cycled product. Granulation of the mass is immediately completed z upon contact with such fines.

The product issuing from the granulator is dried in a rotary dryer in which the temperature should be in the Arange from 70 to 90 C. and then separated into the '.three portions hereinabove described.

lThe cooling can be eiectuated on thewhole mass :issuing from the dryer but it is better to carryl out a rst division of the product into sizes before cooling. It

fis advantageous to recycle the oversized particles as hot :as possible to the concentrator-dissolver. It is also adyantageous to submit the product issuing from the dryer to a first separation on a screen of large mesh. Under these conditions, the screening, even though it is effected upon a hot product, is very easy to accomplish. The product which passes through this iirst screen, that is to say, the iines and the commercial sized particles, is then cooled up to about Ztl-50 C. in order to be easily separated in a second screen into average particles and nes. The nes may be directed to still a third screen, if it is desired, in order to `separate them into larger and smaller lines for separatore-cycling. The medium sized. granules are those which are of commercial size and these are moved into storage, while thenes are divided in accordance with their size, between the mixer and the granulator.

It is advantageous to maintain a constant output and to maintain a constant quantity of material in the recycling.v According to another characteristic of the invention, this is obtained by maintaining the output to storage at a constant delivery rate, returning the whole balance of the output to the process by recycling. In order to accomplish this in the best way the excess of correctly sized product above that which is sent to the storage is finely crushed before being reintroduced into the granulator.

It is an advantage of this process that there is no diriiculty in nely dividing this over-plus of material of correct size. Itis already evenly sized and it is cold, and the ditiiculties which arise in connection with the prior art disintegration of the oversized particles has been discovered not to exist. Furthermore, this crushing or grinding only involves a relatively small portion of the product, if any, and involves none at all when the process is perfectly regulated.

In the following example there is a description of the invention as applied to the manufacture of a fertilizer containing about 12% nitrogen, 12% P205, and 20% K2O. The process starts from a phospho nitrate sludge having an ammonium nitrate and dicalcium phosphate base. This sludge is prepared by attacking natural phosphate ,with nitric acid, reducing the ratio of calcium nitrate either by separation of a part or all of Vthe Vsalt orby. adding phosphoric acid, and ammoniating the product. The example is not a limitation but an illustration of the invention, and it is to be noted that the use of phosphoric acid to reduce the ratio of the calcium nitrate is simply exemplary, as other acids, for instance sulphuric acid, can be used forr the same purpose.

The invention is also capable of being applied to the fabrication of binary fertilizers, for example, those containing 20% of nitrogen and 20% P205 without potassium. The process may be used, also, for making any kind of fertilizer, even simple, single constituent fertilizer. The optimum concentrations of water in the sludge at the beginning, and the optimum temperatures will diier somewhat with different fertilizers and will be determined in the plant while remaining within the general principles herein set forth, which are applicable to all fertilizers which are produced by a process involving granulation.

The accompanying drawing is a schematic diagram and flow sheet of a novel apparatus employed to carry out the process set forth in the following example. Both apparatus and process will'be described in the example.

ExampIe.-Nitric acid was used to attack natural phosphate from Morocco at a rate which produced a phospho-nitrate sludge at a rate of eight metric tons per hour. This sludge was ammoniated after it had been stripped of calcium nitrate; removalv was Vaccomplished by filtering olf a part of the salt and adding phosphoric acid to change the form of the remainder. The sludge required about one percent of its weight of ammoniacal nitrogen to be brought to its final condition for use in the present invention. Tlie'sludge obtained titrated 15% P205, 6.5% nitric acid, 5.5% ammoniacal nitrogen, and 28% water. Its temperature was on the order of 105 degrees C. This sludge 'was poured into a vat 1, provided with an agitator, shown, but not numbered, through a conduit 2,' the rate of 'addition to the vat being, as stated, about 8 metric tons per hour; at the same time, 5 tons per hour of oversized product were discharged from the end of the process 'and added toA the vat through a conduit 3. This recycled product was still hot from the dryer. Through a submerged inlet 4, 100 kilograms per hour of gaseous lammonia were admitted to the vat. The ammoniation was exothermic and contributed to compensate for the chilling eect of theV dissolving oversized granules. Thus, the temperature remained constant while the dimensions of the oversized particles were reduced by the dissolving of the outer parts of the granules." In the rpresent case, it was desired to produce granules having a maximum dimension of 4 millimeters and this was accomplished with the rates` of addition specified. The materialwas not totally dissolved. It was also desired that the particle size should not be less than 2 millimeters andthe process of size reduction generally stopped above that limit.

It is to be understood that the size could have been selected as desired. The temperature remained substantially constant without the addition of heat, other than that produced by the ammoniation reaction and the temperature of the material from the drier.

The sludge thus formed was discharged, again at about V8 tons per hour, to one end of a long tank`6 provided with a worm-type conveyor, shown'but not numbered, which performed a double function ofsecuring good mixing of the ingredients and of constantly moving the mass toward the discharge end. The concentrator-dissolver 6 had a capacity of about 1.5 cubic meters and it received in addition to the discharge from vat 1 about 5 tons per hour of the oversized, re-cycled granules, while still hot, from the dryer. In this apparatus the temperature was maintained constant at about a blast of hot air being admitted to the top of the mass through a pipe 8; the air was at about 250 C.

The sludge issuing from the concentrator-dissolver by overiiow was admitted to a mixer'9 where it was mixed with about 10 tons per hour of lines of dimensions less than 2 millimeters arriving by a conduit 10.

The fines .were introduced, `recycled, .at a temperature of `about A.30," .C. and no other vcooling was necessary to assll@ ithe. crystallization of the sludge in the mixer. If, onthecontrary, the .lines `were introduced hot from the dryer, it was advisablelo chill the product in the mixer by a `blast of ,cold air issuing from discharge nozzles 11 in order to .keep the temperature below 70 C. inlhc mixer. The paste thus formed in this way was then `introduced into a granulator 12 .which was of high speed type. There was also admitted ,to this granulator through thc .conduit l13 Vabout four tons per hour of PQaSsium chloride titrating about 52% K2O, thus making the finished product a ternary fertilizer. A surplus of lfinely divided finished product, being the quantity of nishcdproduct above `a selected, uniform discharge rate fortheapparatus, was admitted to this granulator through pipe 14 after preliminary crushing in crusher 22 to the size of 4fines. In Athis way, ,the output of commercial product ,was maintained .constant in spite of accidental variations and changes in production rate.

From the ,granulator 12, the product went to a dryer 15 and from ,the dryer v.to a coarse screen 16 for the purpose of `separation into sizes. The screen retainedparticles largerthan 4 millimeters in size, vand passed those of smaller dimensions to cooler 17, from which they went toa second screen 18, which passed particles smaller than 2 millimeters and retained those above that size.l One-third ofthe total product issuing from the granulator and dryer was composed of oversized granules (in' this case, larger than 4 millimeters) one-third was between 2 and V4 millimeters, that is, of average or commercial size, andvone-third was composed of fines (in this case, smaller ythan 2 millimeters).` The oversized particles from screen 16 were re-cycled through conduits 3 and 7 as hereinbefore described. The ncs which passed screen 18 were sent to the head end of the mixer 9. The medium sized particles from screen 18 were sent to' a uniform-discharge device 19, which directed finished productto storage at a uniform rate. The surplus from this rate of discharge .to storage was sent to afcrusher 22 where it Was reduced to a staterof fines and these were added Vthrough conduit 14 to the granulator 12.

As above stated,the lines from screen 18 can be divided between the mixer 9 and the granulator 12 and the totaLproduct of `medium size may be sent to storage, .ibut a superior operation of the apparatus and processes is obtained 'by `discharging to storage less than the total output of the apparatus, the surplus being reduced in size and re-crycled as hereinbefore described.

Inthe present example, ten tons per hour of oversized granules were obtained, wlib/were re-cycled while still hot, going into thv vat 1 and 50% into the concentratordissolver 6. There-went through the screen 16, composed of 'mediums and `fines, 20 tons per hour which were cooled to 30 degrees C; in the cooler .17 "and lthen separated on the screen 18.' This produced l0 tons per hour of granules between 2 and 4 millimetersin sizefand ten tons of lines less rthan 2 millimeters in size which were returned to the mixer 9. The discharge apparatus 19 was regulated to Vdischarge automatically ten tous per hour to storage, any excess above this falling by overliow into a crusher 22 of hammerrnill typefl Y i lThe product issuing from the hammermill was very fine `was reintroduced into nthe granulator 12 down s't'ieznarn* of theppint'of introduction of `potassium chloride. T he hammermill hada capacity of 'three tons per hour, Xwhich was sufficient, and corresponded to about 30% .with respect to the' normal rate of production of the apparatus. yThis represents a material reduction in size of thecrushing apparatus which was required byxtlilezprior artrin similar processes and which had Vof necessity of minimum outputof Vten tonsper hour of 8. finely divided material. This ,represents a material sav,- ing in capital investment.

The process and Yapparatus `described in .this example produced ten tons per hour of granulated product with `a reduction of vre-cycled product of about 20 tonsper hou'r,`

that is to say, that the prior art process starting withllike raw materials required the re-cycling of 2Q tons penhour more of nished product than does the process ofAthis invention. Another advantage is that the crushing of in:V

sufficiently dried product, which was a characteristicgof the prior art, isdone away with. The invention also the advantage of eliminating the preliminary conceng tration of the sludge. A particular advantage is rthat the regularity ofthe process is much improved and automatically maintained by means of the automatic regulation of discharge to the stock andthe re-cycling of the surplus.

Although the invention is particularly concerned l,vi/ith j fertilizers and their manufacture, it is applicable to simiof the granules, the iinest particles Vbeing added lastV and` in a stage of the process where the concentration of solids in the sludge is relatively high, so that the tine particles are capable of being enlarged by accretion of part of the solids in the sludge.

In the process generalized in the preceding paragraph,

the product issuing from the process is divided into` a product having the desired dimensions, a product having Y oversized dimensions and a product having undersized dimensions, the oversized being re-cycled tothe sludge at a state where it still contains enough water to dissolve l a part of the product and reduce its dimensions to atsize equal or less than the largest which `is desired in the final product; the lines being' added to the sludge at a stage later than the foregoing, and at which the sludge is ca.

pable of crystallizing upon tine particles and increasing their dimensions.

As it is frequently the case that the dissolving of a final product and initial sludge is accompanied by a reduction in temperature, the temperature is maintained;

at a value advantageous to the reactions proceeding yin the sludge, either by introducing heat from an externalsource or by exothermic chemical reactions accomplished in situ, the external application of heat being, for example, *by blasts of hot air directed upon the sludge, or by heating one or another of the ingredients which are to be; adl In one manner of executing the invention, re-cycled product is brought hot from the: heated rotary drum ,in which drying of the product is mitted to the sludge.

accomplished; this is advantageous in the fertilizer industry.

At the stage of the process in which line particlesare re-cycled to the sludge, the temperature is maintained, at the time of admission of the nes, at a temperature favorable tothe crystallization of the product upon line particles. The temperature may be maintained either by cool-V ing the lines prior to their admissionto the apparatus or by a blast ofcold air directed upon the sludge. These various cooling means maybe combined whenever it is advantageous.

When the sludge has received lthe oversized particles and some of the nes which have been re-cycled, after size classiiication, it may also receive any solid material` which is desired in the fini-shed product and which-does` not react chemically with the ingredients of the sludge,

to change the character thereof. In the manufacture'of fertilizers, a binary sludge may be made into la ternary fertilizer by the addition of an element which is notormally present in the sludge as it comes from the acid opening of the natural phosphate. An example is the addition of potassium salt to a phospho-nitrate fertilizer. On the other hand, additional quantities of the finished product may be admitted, after diminution if desired.

Generally speaking, it is desirable to readmit the oversized particles While they are still hot from the drier. This is invariably so in the manufacture of fertilizer, to compensate for the cooling effect of the heat of dissolution. The superior control of the regularity of the process can be maintained by directing to stock somewhat less than the totality of the finished product, the excess being re-cycled with or without preliminary reduction in size. Preferably, the product thus re-cycled is divided by crushing or grinding and cooled before readmission to the process.

A particularly advantageous employment of the principles of the invention is found in the manufacture of phospho-nitrate fertilizers, regardless of whether the attack upon the phosphate of fertilizer grade is accomplished by nitric acid alone or by nitric acid in combination with other acids. The process is particularly -advantageous when the said attack is followed by an ammoniation.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

VWhat is claimed is:

1. A process of making fertilizer from a Sludge resulting from the attack by nitric acid on natural phosphate of fertilizer grade from which calcium nitrate has been removed and to which ammoniacal nitrogen has been added and which comprises about 28% Water, which comprises mixing ammonia with the sludge, simultaneously adding thereto hot, oversized granules, as hereinafter defined, taken from the fertilizer produced by the process, while maintaining the sludge at about 105 degrees C., removing a part of the product thus produced and adding thereto additional quantities of said hot, oversized granules While maintaining said part at about 90 degrees C., mixing the product with enough cold, undersized particles, as hereinafter defined, taken from the fertilizer produced by the process, to produce a paste, while maintaining the temperature under 70 degrees C., mixing the paste thus formed with disruptive agitation with potassium chloride and with finely divided fertilizer derived from the product produced by the process, drying the product, separating it into parts having dimensions on the order of 2 to 4 millimeters, dimensions over that size and dimensions under` that size, and re-cycling the parts having oversized dimensions to the process steps as hereinbefore indicated.

. 2. A process of making fertilizer from a sludge resulting from the attack by nitric acid on natural phosphate of fertilizer grade from which calcium nitrate has been removed and to which ammoniacal nitrogen has been added and which comprises about P205, 6.5% nitric acid, 5.5% ammoniacal nitrogen and 28% water, which comprises mixing ammonia with the sludge, simultaneously adding thereto hot, oversized granules, larger than about 4 mm., taken from the fertilizer produced by the process, while maintaining the sludge at about 105 degrees C., removing a part of the product and adding thereto additional quantities of said hot, oversized gran- -f ules while maintaining said part at about 90 degrees C., mixing the product with cold, undersized particles, slightly less than about two millimeters `in size, taken from the fertilizer produced by the process, while maintaining the temperature `under 70 degrees C., mixing the paste thus formed, with disruptive agitation, with potassium chloride and with more, finely divided fertilizer derived from the product produced by the process, drying the product, separating it into parts having dimensions on the order of 2 to 4 mm., oversized dimensions, and undersized `10 dimensions, and re-cycling the parts having oversized and undersized dimensions to the process steps as hereinbefore indicated. Y v

3. The steps in the process of making fertilizer from the sludge resulting from the attack of acid on phosphate of fertilizer grade Which comprises recycling to the said sludge from the final product of the process, particles of size too large to be desired in the commercial product, the addition being made to a said sludge containing water sufcient to reduce the size thereof by dissolving such teo-large particles until their dimensions are reduced to those desired in the commercial product, adding to the product thus produced particles of fertilizer, derived from the final product, having dimensions less than those desired in the commercial product, granulating and drying the iinal product, and separating therefrom the parts of commercial size. 4. A process of making fertilizer from a sludge resulting from the attack by acid on phosphate of fertilizer grade which contains about 28% water, which comprises adding to the said sludge granules of fertilizer, produced by such process, too large to be desired in the commercial product, While maintaining the sludge at about to degrees C., mixing the product with particles of fertilizer, produced by the process, too small to be desired in the commercial product while maintaining the temperature under about 70 degrees C., mixing the paste thus formed with disruptive agitation with nely divided particles of such fertilizer, drying the product with heat, separating it into parts having dimensions desired in the commercial product, dimensions too large for the commercial product and dimensions too small therefor, and recycling the parts having the too-large and the toosmall dimensions as aforesaid.

5. A process of making fertilizer from a sludge resulting from the attack by acid on phosphate of fertilizer grade which contains suflicient W-ater to reduce the size oftfertilizer granules produced by the process, which comprises adding to such sludge hot granules, taken from the fertilizer produced by the process, which are too large for the commercial product, while maintaining the sludge at about the boiling temperature of water, mixing the product with cold particles taken from the fertilizer produced by the product, which-=are too small for the commercial product, while maintaining the temperature -under 70 degrees C., mixing the paste thus formed, with `disruptive agitation, with nely divided fertilizer derived from the product produced by the process, drying the product, separating it into parts having dimensions desired in the commercial product, dimensions too large therefor and dimensions too small therefor, cooling the parts having the too small dimensions, and recycling the said too large and too small parts to the steps hereinbefore indicated, the parts having too-large dimensions being recycled While still hot.

6. A process of making fertilizer granules of commercial sizes from a sludge resulting from the attack by acid, comprising nitric acid, on phosphate of fertilizer grade, which sludge contains suiiicient Water to reduce the size of fertilizer granules produced by the process, which comprises mixing ammonia with the saidwatery sludge, simultaneously adding thereto hot fertilizer granules of size too large to be included in such commercial sizes, taken from the fertilizer produced by the process, while maintaining the sludge at `about 90 to 105 degrees C., mixing the product of such addition with enough cold particles, taken from the fertilizer produced by the process, too small to be included in such commercial sizes, to form a paste, while maintaining the temperature under 70 degrees C., mixing the paste thus formed with disruptive agitation with suicient additional finely divided fertilizer, derived from the product produced by the process, to produce granulation, drying the product, separating it into parts having dimensions desired in the commercial product, dimensions too large, and dimen- 111 sionsL too" smallv forY such commercial product, recyclingl the said too=large parts, as aforesaid, While still'hot from the drier, cooling the too-small parts, and recycling the sa'idA too-smallV parts, as aforesaid.

7l A process of making fertilizer from a sludge resultingfrom the attack by acidcomprising nitric-acid on phosphate of fertilizer grade from which calcium nitrate has been removed and which contains sufficient water to reduce` the size of fertilizer granules produced by the process, which comprises mixing'ammonia with the said watery sludge, simultaneously adding'thereto hot granules of such fertilizer as isproduced by the process, in sizes too large to be'desired in the commercial product, While maintaining the sludge at aboutv 90'to 105 degrees C., mixing the product of such addition with particles taken from the fertilizer produced by the process, in sizes too small to be desired inthe commercial product, While maintaining the temperature under 70 degrees C.,

mixingthe paste thus formed with disruptive agitation with` sufiicient finely divided fertilizer ofthe type produced by the process toA produce granulation, drying the product, separating it into parts having dimensions desired p in the commercial product, parts too large and parts too small therefor, and recycling the toolarge parts and too small-parts tothe process steps as hereinbefore indicated.

8. A process of making fertilizer from a sludge resulting from the attack by acid comprising nitric acid p onl phosphate of fertilizer grade from which calcium nitrate has been removed and which contains sufficient Water to reduce the size of granules of fertilizer such as is produced by the process, which comprises mixing ammonia with the sludge, simultaneously adding thereto hot granulesof fertilizer such as is produced by the process, in sizes too large to be desired in the commercial process, while maintainingV the sludge at about 90 to l05 degrees C., mixing the product with cold particles of such fertilizer as is produced by the process in sizes too small to be desired in the final product, while maintaining the temperature under 70 degrees C., in quantity sufiicient to form a paste, mixing the past thus formed with disruptive agitation with a fertilizer component, and With finely divided fertilizer derived from the product produced by the process, drying the product thus produced, separating it into parts having dimensions desired in the commercial product, andv into dimensions too large and too small therefor, and recycling the too large and too small dimensions to the process steps as hereinbefore indicated.

9; A process of making fertilizer fromr a sludge resulting from the Iattack of nitric acid on phosphate of fertilizer grade from which calcium nitrate has been removed and which comprises about 28% water, which comprises mixing ammonia with the sludge, simultaner ously adding thereto hot granules, too large for the commercial product, takenV from such fertilizer as is produced by the process,.while maintaining the sludge at about 105 degrees C., removing apart of the product thus formed and adding thereto additional quantities of said" hot, too-large granules While maintaining said part at about 90 degreesY C., mixing the product of such addition with enough cold particles, taken from the fertilizer produced by the process, in sizes too small to be included in the finished product, to form a paste, while maintaining the temperature under 70 degrees C., mixing the paste thus formed with disruptive agitation with a potassiumcontaining fertilizer component and with finely-divided fertilizer derived from the product produced by the process, drying the product thus produced, separating it into parts having dimensions desired in the commercial product, dimensions too large therefor andy dimensions too small,` and recycling the too large andtoo sm'all dimeti-V sions to the process steps' as hereinbefore indicated;V

l0; In the manufacture of fertilizer iii' which" a' ,sludgeJ is formedV by attacking phosphate of'fertilizer grade with acid'comprising nitric acid, the steps that' comprise a'ddl ing to the said sludge from the finished product of the process particles of size Vtoo large to be commercially desired, the addition taking place in the presence in the sludge of Water sufficient to dissolve the said' added-over` sizedA particles sufficiently to reduce their si'ze to that commercially desired, adding afterwards to Vthe sludge from the finished product of the process' particlesof size too small to be commercially desired, granulating` the paste thus formed, separating `the finished product into? particles having the size commercially desired, particles too small and particles too large, and recyclingk the-said too large and too small particles as hereinbeforeiridicated.

ll- The steps in the process of making fertilizerfrornthe sludge resultingfrom the attack by acid comprising nitric acid on phosphate of fertilizer gradeY and subse quent addition ofl ammonia, that comprise: adding-to the said sludge fromthe finishedp'roduct ofthe process oversized particles, Vi. e., particles of size too large'to-,be i commercially desired, the addition takingl placetin theY presence in the sludge ofwater sufiicient to'dissolveV .thev

said added oversized particles sufiiciently toreduce-their' size to that commercially desired, and While maintaining the sludge at about to 105 degrees C., adding after-` wards to the sludge from` the finished product of the process undersized particles, i. c., particles of si'zetoosmall to be commercially desired, while rrrai1`1taining'theV temperature under 70- degrees C., mixing the pasteD thus? formed with disruptive agitation withnely divided fertilizer derived from the finished product ofl the process, granulating the paste thus formed, separating the finished product into particles havingV commercially desired size,A oversized and undersized particles, and recycling the sa'id oversized #and undersized particles as hereinbeforegindii t cated- 12. Apparatus for the manufacture of fertilizer com= prising a size reduction and ammoniation'vat, aV dissolve` t ing and concentrating vat connected to the saidammoniation vat to receive the discharge therefrom, meansl to heat the concentratorvat, a mixer vat connected with the concentrator vatv to receive the discharge therefrom, means to cool the mixing vat, a granulator connectedl with the said mixer to receive they discharge therefrom, a drier connected with the granulatorto receive thedis-l charge therefrom,- a coarse Lscreen connected" Withtle drier to receive the dischargetherefrom, meansv to transfer` the particles rejectedby the coarse screenvtothe said ammoniation and concentrator vats, means to transfer the particles passed by the coarse screeny to a cooler, means to transfer the material in the cooler to affine screen, means to transfer the material passed by thefne screen to the said mixer, meansvto transfer thefmaterial of medium size rejected bythe fine screen to a selector of uniform output, means to transfer the over-plus from,` the selector to a crusher, and means to transfer the material from the crusher to the. saidA granulator.

References Cited inzthe file of this patent UNITED' STATES PATENTS 709,185 Teme Sept; 16, 1902V v1,999,026 Tramm et al. Apr. 23, 1935v 2,015,384 Nordengren Sept. 24, 1935 2,167,432 COX et al. July 25, 1,939 2,448,126 Shoeld Aug. 31,1948* 2,598,658 Procter et al. May 27,' 1952., 

1. A PROCESS OF MAKING FERTILIZER FROM A SLUDGE RESULTING FROM THE ATTACK BY NITRIC ACID ON NATURAL PHOSPHATE OF FERTILIZER GRADE FROM WHICH CALCIUM NITRATE HAS BEEN REMOVED AND TO WHICH AMMONIACAL NITROGEN HAS BEEN ADDED AND WHICH COMPRISES ABOUT 28% WATER, WHICH COMPRISES MIXING AMMONIA WITH THE SLUDGE, SIMULTANEOUSLY ADDING THERETO HOT, OVERSIZED GRANULES, AS HEREINAFTER DEFINED, TAKEN FROM THE FERTILIZER PRODUCED BY THE PROCESS, WHILE MAINTAINING THE SLUDGE AT ABOUT 150 DEGREES C., REMOVING A PART OF THE PRODUCT THUS PRODUCED AND ADDING THERETO ADDITIONAL QUANTITIES OF SAID HOT, OVERSIZED GRANULES WHILE MAINTAINING SAID PART AT ABOUT 90 DEGREES C., MIXING THE PRODUCT WITH ENOUGH COLD, UNDERSIZED PARTICLES, AS HEREINAFTER DEFINED, TAKEN FROM THE FERTILIZER PRODUCED BY THE PROCESS, TO PRODUCE A PASTE, WHILE MAINTAINING THE TEMPERATURE UNDER 70 DEGREES C., MIXING THE PASTE THUS FORMED WITH DISRUPTIVE AGITATION WITH POTASSIUM CHLORIDE AND WITH FINELY DIVIDED FERTILIZER DERIVED FROM THE PRODUCT PRODUCED BY THE PROCESS, DRYING THE PRODUCT, SEPARATING IT INTO PARTS HAVING DIMENSIONS ON THE ORDER OF 2 TO 4 MILLIMETERS, DIMENSIONS OVER THAT SIZE AND DIMENSIONS UNDER THAT SIZE, AND RE-CYCLING THE PARTS HAVING OVERSIZED DIMENSIONS TO THE PROCESS STEPS AS HEREINBEFORE INDICATED. 